Chapter 4 Reactions in Aqueous Solutions. Types of Chemical Reactions Chemical Reactions discussed in College Chemistry can be broken down into 3 main.

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Presentation on theme: "Chapter 4 Reactions in Aqueous Solutions. Types of Chemical Reactions Chemical Reactions discussed in College Chemistry can be broken down into 3 main."— Presentation transcript:

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Types of Chemical Reactions Chemical Reactions discussed in College Chemistry can be broken down into 3 main categories –Precipitation reactions –Acid-Base reactions –Oxidation-Reduction (redox) reactions

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Types of Chemical Reactions Precipitation Reactions: A process in which an insoluble solid (precipitate) drops out of the solution.Precipitation Reactions: –Clear solutions of two ionic compounds when mixed form a cloudy solution (cloudiness indicates solid)

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Types of Reactions Acid–Base Neutralization: A process in which an acid reacts with a base to yield water plus an ionic compound called a salt. –The driving force of this reaction is the formation of the stable water molecule.

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Types of Reactions Oxidation–Reduction (Redox) Reaction: A process in which one or more electrons are transferred between reaction partners. –The driving force of this reaction is the decrease in electrical potential.

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Precipitation Reactions Develop the reaction equation Balance the reaction equation Predict the state of matter of each species present

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Precipitation Reactions and Solubility Rules To predict whether a precipitation reaction will occur must be able to predict whether a compound is soluble or not –Solubility rules

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Precipitation Reaction Precipitation reactions only occur if a solid is produced as a product. If all products are aqueous compounds then no reaction has taken place.

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Electrolytes in Aqueous Solution To discuss aqueous reactions, must understand how different compounds interact with water Electrolyte – substance that when added to water dissociates to form ions allowing for conductivity –Strong electrolytes – completely dissociate –Weak electrolytes – partially dissociate –Non-electrolyte – no dissociation in water

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Aqueous Reactions and Net Ionic Equations Molecular equations – substances involved in chemical reaction have been written using full formulas Complete ionic equation – shows every species as it truly appears in the reaction vessel (aqueous strong electrolytes are shown as ions) Net ionic equation – shows what is truly taking place in the reaction (all spectators are removed) –Must have a net ionic reaction for the reaction to occur as written

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Electrolytes in Aqueous Solution To discuss aqueous reactions, must understand how different compounds interact with water Electrolyte – substance that when added to water dissociates to form ions allowing for conductivity –Strong electrolytes – completely dissociate –Weak electrolytes – partially dissociate –Non-electrolyte – no dissociation in water

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Acids, Bases and Neutralization Reactions Neutralization Reactions –Complete ionic reactions Strong electrolytes (strong acids and bases) will dissociate entirely Weak electrolytes are not shown as dissociated –Net ionic for strong acids reacting with strong bases will always be for the formation of water

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Oxidation-Reduction Reactions Redox reactions are those involving the oxidation and reduction of species (element or ion of an element). Oxidation and reduction must occur together. They cannot exist alone. Two important types –Single displacement reactions (activity series) –Combustions – reaction of a substance with O 2

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Redox Reactions Assigning Oxidation Numbers: All atoms have an “oxidation number” regardless of whether it carries an ionic charge. 1.An atom in its elemental state has an oxidation number of zero. 2. An atom in a monatomic ion has an oxidation number identical to its charge.

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Redox Reactions 3. An atom in a polyatomic ion or in a molecular compound usually has the same oxidation number it would have if it were a monatomic ion. –A. Hydrogen can be either +1 or –1. –B. Oxygen usually has an oxidation number of –2. In peroxides, oxygen is –1. –C. Halogens usually have an oxidation number of –1. When bonded to oxygen, chlorine, bromine, and iodine have positive oxidation numbers.

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Problem Sodium tripolyphosphate is used in detergents to make them effective in hard water. Calculate the oxidation number of phosphorus in Na 5 P 3 O 10. –A. +3 –B. +5 –C. +10 –D. +15 –E. none of these is the correct oxidation number

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Redox Reactions 5. Whenever one atom loses electrons (is oxidized), another atom must gain those electrons (be reduced). –A substance which loses electrons (oxidized) is called a reducing agent. Its oxidation number increases. –A substance which gains electrons (reduced) is called the oxidizing agent. Its oxidation number decreases.